1. Field of the Invention
The present invention relates to methods for making thermal interface material, and particularly to a method for making carbon-nanotube-based thermal interface material.
2. Discussion of Related Art
Electronic components such as semiconductor chips are becoming progressively smaller, while at the same time heat dissipation requirements thereof are increasing. Commonly, thermal interface material is utilized between the electronic component and an integrated heat spreader/sink, in order to efficiently dissipate heat generated by the electronic component. However, the performance of the thermal interface material is generally restricted by a heat conduction coefficient thereof. The heat conduction coefficient of typical thermal interface units is now considered to be too low for many contemporary applications.
Conventional thermal interface materials are metallic materials. However, the metallic materials disadvantageously tend to have a much higher coefficient of thermal expansion than do semiconductor devices. Mechanical stresses are induced during temperature cycling and will tend to overstress the electronic components, thereby leading to potential failures when metallic materials are used as a thermal interface material.
A recently developed thermal interface material is a composite material obtained by combining carbon nanotube arrays with a polymer or a low melting point metallic material. The carbon nanotubes are orderly distributed and provide a heat conduction path therein. Additionally, the carbon nanotubes can protrude from the polymer or low melting point metallic material and contact the electronic components or the integrated heat spreaders. However, the heat conduction coefficient of the polymer is relatively low. As such, the performance of the thermal interface material is restricted by the polymer used. Since metals generally have a higher heat conduction coefficient than polymers, the thermal interface materials using carbon nanotube arrays combined with low melting point metallic materials have attracted lots of attention, due to the potential for improved heat conduction coefficients.
Methods for making the thermal interface material using low melting point metallic materials combined with carbon nanotube arrays generally have employed chemical vapor deposition or physical vapor deposition. In these methods, the low melting point metallic materials are heated to a gaseous state and deposited in the interspaces between the carbon nanotubes of the carbon nanotube array. However, although some of these metallic materials have a low melting point, they also have a very high boiling point, e.g., the melting point of indium is 157° C. and the boiling point thereof is 2000° C. Thus, the above-described methods consume lots of energy, and the costs thereof are quite high.
What is needed, therefore, is a method for making a carbon-nanotube-based thermal interface material, wherein the low melting point metals just need to be heated to a liquid state.